Birds migrating to and from breeding grounds in the United States and Canada are killed by the millions in collisions with lighted towers and their guy wires. Avian mortality at towers is highly variable across species, and the importance to each population depends on its size and trajectory. Building on our previous estimate of avian mortality at communication towers, we calculated mortality by species and by regions. To do this, we constructed a database of mortality by species at towers from available records and calculated the mean proportion of each species killed at towers within aggregated Bird Conservation Regions. These proportions were combined with mortality estimates that we previously calculated for those regions. We then compared our estimated bird mortality rates to the estimated populations of these species in the United States and Canada. Neotropical migrants suffer the greatest mortality; 97.4% of birds killed are passerines, mostly warblers (Parulidae, 58.4%), vireos (Vireonidae, 13.4%), thrushes (Turdidae, 7.7%), and sparrows (Emberizidae, 5.8%). Thirteen birds of conservation concern in the United States or Canada suffer annual mortality of 1â9% of their estimated total population. Of these, estimated annual mortality is >2% for Yellow Rail (Coturnicops noveboracensis), Swainsonâs Warbler (Limnothlypis swainsonii), Pied-billed Grebe (Podilymbus podiceps), Bay-breasted Warbler (Setophaga castanea), Golden-winged Warbler (Vermivora chrysoptera), Worm-eating Warbler (Helmitheros vermivorum), Prairie Warbler (Setophaga discolor), and Ovenbird (Seiurus aurocapilla). Avian mortality from anthropogenic sources is almost always reported in the aggregate (ânumber of birds killedâ), which cannot detect the species-level effects necessary to make conservation assessments. Our approach to per species estimates could be undertaken for other sources of chronic anthropogenic mortality.

Every year and across the world, thousands of fledglings of different petrel species crash into human structures because they are disorientated by artificial lights during their first flights. As this phenomenon is rather predictable, rescue campaigns are organized to help birds to reach the ocean, but unfortunately, a low proportion gets hurt or dies. Despite the huge number of affected individuals, and the fact that the problem was detected a long time ago, little is known on this source of mortality. We have studied the factors (i.e. body condition, plumage development, fledging date and sex) influencing the mortality of Cory's Shearwater Calonectris diomedea fledglings stranded inland due to light pollution in Tenerife (Canary Islands) during two consecutive breeding seasons (2009 and 2010). Late fledglings showed lower values of a body condition index than early ones. No sex biases were detected, neither considering stranded birds overall, nor for recovery dates or in the body condition of rescued fledglings. Our results indicate that late birds stranded by lights showing abundant down are more susceptible to fatal collisions and that the lights do not selectively kill birds with lower body condition indices. An enhancement of veterinary care should be done during the last part of the fledging period when more fatal collisions occur, especially focused on fledglings with abundant down. More research to determine why some individuals end up disoriented around artificial lights and others do not is urgently needed to minimize or prevent fallouts.

Night migratory songbirds can use stars, sun, geomagnetic field, and polarized light for orientation when tested in captivity. We studied the interaction of magnetic, stellar, and twilight orientation cues in free-flying songbirds. We exposed Catharus thrushes to eastward-turned magnetic fields during the twilight period before takeoff and then followed them for up to 1100 kilometers. Instead of heading north, experimental birds flew westward. On subsequent nights, the same individuals migrated northward again. We suggest that birds orient with a magnetic compass calibrated daily from twilight cues. This could explain how birds cross the magnetic equator and deal with declination.

The transduction mechanisms and the neurophysiological basis of magnetoreception in birds are still largely unexplained, even though the role of the magnetic compass in the orientation of birds is fairly well understood. The discussion on magnetoreception in birds and terrestrial vertebrates focuses mainly on two mechanisms: small particles of magnetite and biochemical bi-radical reactions of excited macromolecules. When the bi-radical hypothesis was first proposed, magnetic resonance phenomena in the retina were suggested as the primary processes, which led to the question of whether magnetoreception was light-dependent. Homing experiments and electrophysiological evidence from pigeons have produced evidence consistent with such a mechanism. An effect of the spectral composition of light on magnetic compass orientation in amphibians has recently been described: under blue light of 450 nm and below, newts oriented as they did under the full spectrum, whereas they showed a roughly 90Â° counterclockwise shift when tested under wavelengths at or above 500 nm. Here we report the first orientation tests on migratory birds under light of different wavelengths; the results suggest a light-dependent process that appears to differ from that reported in newts.